In this example, the curve on the left shows where Zone placement will fall when Zone I is placed at 0.10 over Fb+f and without factoring in flare. The curve on the right takes the 0.10 density placement of the curve on the left, but incorporates a 1 stop flare factor.

Zone and Flare - No flare and 1 stop flare.jpg

What do you think would happen to the Zone placement if instead of having to increase the EI by 2/3 to 1 stop, rate the film at the ISO and then factor in flare?